Preparation

Have ready meringue and cake roll. In a small bowl stir together yogurt, vanilla, and 1 tablespoon sugar.

In a large bowl with a whisk or an electric mixer beat cream and 2 teaspoons sugar until cream just holds stiff peaks. Crumble meringue into 1/2-inch pieces and gently fold into whipped cream. Reserve 1/2 cup raspberries and add remaining berries and yogurt mixture to whipped cream mixture. Gently fold mixture until just combined.

Unroll cake roll on kitchen towel and brush inside with Chambord. Gently spoon whipped cream mixture lengthwise along center of cake and roll cake around filling so that long edges just come together. Place roulade, seam side down, on a platter and chill 1 hour to facilitate slicing.

Just before serving, sprinkle roulade with remaining 2 teaspoons sugar. Cut roulade into slices (each a little less than 1 1/2 inches thick) serve with some reserved berries.

To make chocolate-covered meringue:
Preheat oven to 325°F.

In a bowl with an electric mixer beat whites on high speed until foamy. Add cream of tartar and continue beating until whites hold soft peaks. Add sugar and beat until meringue holds stiff, glossy peaks.

Line a baking sheet with parchment paper or foil and on it spread meringue about 1/2 inch thick (shape does not matter). Bake meringue in middle of oven 45 minutes, or until crisp. Turn off oven and let meringue stand 1 hour. Remove meringue from oven and cool completely on baking sheet on a rack.

Carefully peel parchment paper or foil and put meringue, flat side up, on a work surface. In a small heavy saucepan melt chocolate over low heat, stirring occasionally, and spread on meringue in a thin layer. Chill meringue until chocolate is set, about 10 minutes. (Meringue may be made 1 week ahead and kept in a sealed plastic bag in a cool place.)

To make cocoa cake roll:
Preheat oven to 425°F. and line a greased 17- by 10 1/2-inch jelly-roll pan with wax paper or parchment paper. Butter paper and dust with flour, shaking off excess flour.

In a small saucepan bring water to a boil over moderate heat. Remove pan from heat and stir in cocoa powder and vanilla until smooth.

In a large bowl with an electric mixer beat yolks and 1/3 cup sugar on high speed until pale and thick, about 5 minutes. Add cocoa mixture and beat until mixture is thick again, 3 to 5 minutes. Add flour and salt and beat 1 minute. (If using a standing electric mixer, transfer mixture to a large shallow bowl better suited to folding.)

Stir about one fourth whites into cocoa mixture to lighten and fold in remaining whites gently but thoroughly. Spoon batter into a large pastry bag fitted with a 1/2-inch plain tip and, holding bag with tip about 1/2 inch from surface of pan, pipe lengthwise in side-by-side strips, filling pan. (Alternatively, batter may be gently spread into pan.) Bake cake 8 minutes, or until it springs back when touched lightly in center with finger. Cool cake in pan, covered with a damp kitchen towel, on a rack.

Invert cake onto towel and gently peel off wax paper or parchment paper. Beginning with a long side, roll up cake in towel jelly-roll fashion.